JP2003031409A - Sintered rare-earth magnet having superior corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a rare-earth magnet having superior corrosion resistance. SOLUTION: A sintered R-Fe-Co-Cu(-M)-B system rare-earth magnet (wherein R denotes at least one element of rare-earth elements including Y, and M denotes at least one element among Al, Ga, Nb, and Mn) contains 28 to 35 wt.% of R, 0.5 to 5 wt.% of Co, 0.01 to 0.3 wt.% of Cu, not higher than 0.3 wt.% of M if necessary, 0.8 to 1.2 wt.% of B and remaining Fe as the main components. In grain boundary where an R2 Fe14 B system main phase and an R-rich phase are adjacent to each other, an intermediate phase containing 30 to 60 wt.% of R, 30 to 60 wt.% of Co+Cu, and remaining Fe is formed in a region of 1 to 20 nm from the grain boundary of the main phase toward the center of the R-rich phase and, further, a composition ratio is terms of atomic % satisfies a formula: (Co+Cu)/R=0.5 to 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to R-Fe-Co-
The present invention relates to a Cu (-M) -B-based (R is a rare earth element containing Y, B is boron) -based rare earth sintered material, and particularly to one having excellent corrosion resistance.

[0002]

2. Description of the Related Art As a permanent magnet having a high energy product,
Sm-Co type magnets, R-Fe-B type rare earth magnets and the like are known. Of these, R- represented by Nd-Fe-B
Fe-B rare earth magnets are a resource-rich Nd and Fe.
Since S is a main component, S that uses scarce Sm resources
The cost is lower than that of the m-Co magnet, and the maximum energy product is about 80 to 120 kJ / m ³ higher than the Sm-Co magnet, which is about 240 kJ / m ³ , and is widely used for various electronic devices. It is used.

However, the rare earth magnets have problems that they have high activity, are easily oxidized, and have poor corrosion resistance. Various attempts have been made to improve the corrosion resistance.
Generally, the surface of the magnet is covered with plating, but it has also been attempted to increase the corrosion resistance by changing the additive element. Improving the corrosion resistance of the magnet itself is a very important technique for improving the reliability after coating.

Elements such as Co are generally used as elements for improving corrosion resistance. Co raises the Curie temperature to improve the temperature characteristic, and the R-rich phase into R ₃
The corrosion resistance is improved by using a Co intermetallic compound.
Japanese Patent Laid-Open No. 8-296005, column 4, lines 27 to 29, states that "Co is an element that suppresses the oxidation of the grain boundary phase alloy, and that the temperature dependence of the residual magnetic flux density of the magnet after sintering is improved. Yes. ”

Cu is another element for improving the corrosion resistance. By adding Cu at the same time as Co, the grain boundary phase becomes an R-Co-Cu intermetallic compound, and the corrosion resistance is further increased as compared with the case where only Co is added. For example, in JP-A-6-96928, column 4, line 29 to line 32, "The use of Cu also has the purpose of improving the oxidation resistance during powdering. And the magnetic characteristics are improved. ”

However, the above-mentioned JP-A-6-96928 is used.
The purpose of the publication is to reduce the coercive force to a low level, so that the irreversible demagnetization can be suppressed to a low level even in a relatively high temperature range.
In Japanese Patent No. 5 publication, the purpose of adding Co is that the rare earth magnet alloy has a fine structure with good pulverizability, and R _{2 is} easily pulverized.
Since there are a large amount of T ₁₇ phase and R ₂ T ₁₄ B phase, the particle size after pulverization can be made small, and the particle size distribution is also good, resulting in good dispersibility of the R-rich alloy in the sintered magnet, It is intended to improve the sinterability and improve the magnet characteristics. As described above, although there are many descriptions as a rare earth sintered magnet to which Co and Cu are added, the optimum microstructure state when Co and Cu are added together has not been known.

[0007]

The corrosion of rare earth magnets is
Since the rare earth element (R-rich phase) existing at the grain boundaries is active, oxidation proceeds from this R-rich phase and spreads throughout the magnet. Therefore, how to protect the rare earth element in the R-rich phase from oxidation without deteriorating the magnetic properties is an important issue. The inventors of the present application devised the present invention by devising how the composition and distribution of the R-rich phase should increase the corrosion resistance in order to obtain a rare earth magnet having excellent corrosion resistance.

[0008]

Means for Solving the Problems The inventors of the present invention realized the present invention by taking the above-mentioned composition of components and finding that the compositional distribution at the grain boundary is particularly important for improving the corrosion resistance. Specifically, R (at least one kind of rare earth element including Y) in weight%: 28 to 35%, Co:
0.5 to 5%, Cu: 0.01 to 0.3%, and if necessary, M (at least one of Al, Ga, Nb, and Mn): 0.3% or less, B: 0.8 to 1 0.2%, balance Fe
The A R-Fe-Co-Cu ( -M) -B based rare-earth sintered magnet whose main _component, the grain boundary of the main phase and the R-rich phase of R 2 _{Fe 14} B system adjacent the main In the region of 1 to 20 nm from the grain boundary of the phase toward the center of the R-rich phase, the main component is R: 30 to 60%, Co + Cu: 30 to 6
It is characterized by having an intermediate phase of 0% and the balance being Fe, and having a composition ratio converted to atomic% of (Co + Cu) /R=0.5 to 2. R + (Co + Cu) in this intermediate phase
The combination of + Fe has a mass% of almost 100%.

As described above, by segregating Co and Cu around the R-rich phase to form an intermediate phase, the surrounding Co
It is considered that the corrosion resistance of each R-rich phase is improved by coating with Cu and Cu. Particularly, if the amount of Dy added in the rare earth sintered magnet is 5% or less by weight, Co
The amount of segregation of Cu and R in the R-rich phase is increased, and the contribution to corrosion resistance can be enhanced. Preferably 3% or less, and more preferably 2% or less are good for segregating. If the Dy amount is 5% or less, 2 between the entire main phase and the R-rich phase
An intermediate phase is recognized in about a part. The amount of Dy is still 2%
If it is less than 80%, an intermediate phase of Co and Cu segregation is recognized in about 80% of the R-rich phase.

1 and 2 are enlarged schematic views of the main phase, R (Nd) rich phase and grain boundary phase of the crystal. FIG. 1 shows the present invention, and FIG. 2 shows the conventional one, which will be described with reference to these two figures. 1 is a main phase, 2 is an R-rich phase, 3 is a grain boundary, 4 is an (R + Co + Cu) -based alloy (intermediate phase), 5 is a magnet surface, 6 is air, and 7 is oxygen. In the conventional type shown in FIG. 2, since the R (Nd) -rich phase 2 is not surrounded by the intermediate phase, oxygen contained in the atmosphere 6 enters from the grain boundary 3 and progresses the oxidation. On the other hand, the R (Nd) -rich phase 2 shown in FIG.
Since it is surrounded by the intermediate phase 4 of (o + Cu) system, there is a part that is oxidized from the grain boundary 3 that is in contact with the atmosphere 6, but the oxidation is blocked by the intermediate phase 4 and the internal grain boundary 3a is reached. Oxidation does not proceed. Therefore, the magnet of Example 1 has excellent corrosion resistance.

As a method of adding an alloy for improving corrosion resistance,
A so-called 1-alloy method, which is added in the melting stage of the raw material alloy, and a 2-alloy method (blending method), in which a predetermined alloy is mixed after coarse pulverization or fine pulverization, are used. In the two-alloy method, elements such as Co and Cu that contribute to corrosion resistance are added to an R-rich alloy for the purpose of preventing powder oxidation, and in particular, the R-rich alloy is made into an intermetallic compound having a specific crystal structure. , It is known to increase the oxidation resistance of alloy powders. Further, with the intention of concentrating elements such as Al and Ga that contribute to the improvement of the coercive force in the grain boundary phase, these elements are added to the R-rich alloy side.

However, if Co or Cu is added to the R-rich phase, even if an intermetallic compound is formed, the oxidation resistance is inferior to that in the case of effective addition. Therefore, by making the total amount of (Co + Cu) to be added the same and changing the ratio of addition to the main phase alloy and the R-rich alloy, the composition ratio in the region near the grain boundary can be made a desired ratio. That is,
The amount of (Co + Cu) added to the main phase alloy is larger than the amount added to the R-rich alloy. Especially Cu is
It does not form a solid solution in the R ₂ T ₁₄ B phase (T: transition metal) and tends to segregate into an R-rich grain boundary phase. Co is 90% main phase, R
Although the rich phase is mixed at a rate of 10%, segregation is larger in Cu when considering the volume ratio of the main phase and the R rich phase. Cu
Is dissolved in the main phase only in about 20 to 30%, and the rest is segregated to the R-rich phase side. (Co + Cu) diffuses and infiltrates from the main phase to the R-rich phase, and the composition near the grain boundary contains more intermetallic compounds than the central part of the grain-boundary phase of the R-rich phase, increasing corrosion resistance. It will be. Further, if the total amount of Co and Cu is increased, the corrosion resistance may be improved, but the magnetic properties are deteriorated, and the value as a high performance magnet is lost.

In the present invention, R is at least one kind of rare earth element containing Y, and Nd, Pr and Dy are preferable. Nd and Dy may be used alone, but a mixture of Nd and Pr may be added to N
It may be used instead of d. R of the main phase alloy, which is the main component, is% by weight, and if it is less than 28%, the liquid phase becomes insufficient, resulting in poor sintering, and if it exceeds 35%, the residual magnetic flux density decreases, so the addition amount is 28-35%. To do. B of the main phase alloy is 0.
If it is less than 8%, the R ₂ T ₁₇ phase will appear, and the coercive force will decrease sharply.
~ 1.2%.

When at least one of Al, Ga, Nb and Mn is added to the main phase alloy, the content is 0.3% or less.
Although the coercive force is improved by adding the above elements,
If it exceeds 0.3%, the decrease in the residual magnetic flux density becomes large, which is not preferable, so the upper limit is made 0.3%.

The amount of Co added to the R-rich alloy is preferably half or less than 0.5 to 5% added to the main phase alloy. Similarly, regarding the amount of Cu added, it is preferable to add less than half of the amount of 0.01 to 0.3% added to the main phase alloy.

The R of the R-rich alloy may be basically the same as that of the main phase alloy, but it may be slightly different due to alloy procurement, lot variation, and the like. Same composition range as main phase alloy R: 28
~ 35%. When the B content of the R-rich alloy is 0.8% or more, the effect of suppressing the generation of coarse particles becomes small, resulting in a decrease in coercive force and deterioration of squareness. Therefore, 0.
Although it is less than 8%, it is preferable not to add B. Ga, Al, Nb, and Mn of the R-rich alloy are basically the same as those of the main phase alloy, but may be slightly different due to convenience of alloy procurement, lot variation, and the like. Ga, Al, N
When at least one of b and Mn is added, the composition range is 0 to 0.3% like the main phase alloy.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. (Example 1) Weight%, Nd23.6%, Pr7.0
%, Dy1.6%, B1.2%, Ga0.07%, Co
An alloy consisting of 2.5%, Cu 0.2% and the balance Fe was cast by the strip casting method. After charging this alloy into a processing container and subjecting it to a heat treatment at 1000 ° C. for 2 hours in a vacuum,
It was crushed by the hydrogen storage method to obtain a raw material coarse powder for the main phase alloy.

Next, in% by weight, Nd 18.6%, Pr
5.2%, Dy8.5%, Co2.0%, Cu0.1
%, Al0.07%, and the balance Fe were similarly used as the raw material coarse powder of the R-rich alloy.

Main phase alloy coarse powder 8
0 mass% and R-rich alloy coarse powder 20 mass% were put into a V-type mixer and mixed for 15 minutes. This mixed coarse powder was pulverized by a jet mill using nitrogen high pressure gas so that the average particle diameter was 4.7 μm. While orienting the obtained mixed fine powder in a magnetic field of 0.6 MA / m, about 100
It was molded at a pressure of MPa. The obtained compact was sintered in vacuum at 1060 ° C, 1080 ° C, or 1100 ° C for 2 hours. Next, these sintered bodies were further heat treated in an Ar atmosphere at 900 ° C. for 1 hour, and then further 48
Heat treatment was performed at 0 ° C. for 1 hour. After observing the appearance of the sintered body, the magnetic properties were measured. Both are Br1.3 on average
6T, Hcj 1.17 Ma / m was obtained.

(Comparative Example 1) By weight%, Nd 23.6%,
Pr7.0%, Dy1.6%, B1.9%, Ga0.0
An alloy consisting of 7%, Co1.5%, Cu0.2% and the balance Fe was cast by the strip casting method. This alloy was placed in a processing container, heat-treated at 1000 ° C. for 2 hours in vacuum, and then crushed by a hydrogen storage method to obtain a raw material coarse powder for a main phase alloy.

Next, in% by weight, Nd 18.6%, Pr
5.2%, Dy8.5%, Co2.5%, Cu0.3
%, Al0.07%, and the balance Fe were similarly used as the raw material coarse powder of the R-rich alloy.

These two types of alloy coarse powder are used as main phase alloy coarse powder 5
0 mass% and 50 mass of R-rich alloy coarse powder were put into a V-type mixer and mixed for 15 minutes. This mixed coarse powder was jet milled with nitrogen high pressure gas to give an average particle size of 4.7.
It was pulverized to have a size of μm. The obtained mixed fine powder is 0.6
Molding was performed at a pressure of about 100 MPa while orienting in a magnetic field of MA / m. The obtained molded body is 106 in vacuum.
Sintering was performed at 0 ° C., 1080 ° C., or 1100 ° C. for 2 hours. Then, these sintered bodies were subjected to 9
After heat treatment at 00 ℃ × 1 hour, 480 ℃ × 1
Heat treatment was applied for an hour. After observing the appearance of the sintered body, the magnetic properties were measured. Both average Br1.36T, Hc
j 1.17 Ma / m was obtained.

Next, the sintered magnets of Example 1 and Comparative Example 1 were tested with a pressure cooker test (PCT) tester 39.
Corrosion was performed under the conditions of 3K, 100% RH, and 203 kPa (2 atm), and after removing the corrosion product on the surface, the weight was measured to determine the amount of mass reduction per unit area. In Example 1 and Comparative Example 1, after 24 hours, 48 hours, 72
Comparing time, 96 hours, and 120 hours,
In Example 1, the weight reduction amount (mg / cm ² ) was
It was 0.4, 0.7, 1.2, 1.6, 1.9,
In Comparative Example 1, 0.6, 1.15, 1.47, 1.
8 and 2.05 were found to be corroded as much as 50% to 10% of those in Example 1.

As a result of detailed examination of the vicinity of the grain boundary between Example 1 and Comparative Example 1, it was found that the addition states of Co and Cu were different between Example and Comparative Example. That is, since a smaller amount of R-rich alloy is added to the main phase alloy, Co and Cu-based alloys are less likely to exist around the Nd-rich phase near the grain boundaries, and Nd at the grain boundary cannot be protected. Example 1
In addition, since the main phase alloy was added more than the R-rich alloy, Co and Cu-based alloys were likely to be generated around the Nd-rich phase near the grain boundary, and the Nd-rich phase had an R + Co + Cu intermetallic compound thickness of about 10 nm. Well, I found out that it was surrounded.

FIG. 3 is a microstructure observation photograph of the R-rich phase portion of the sintered magnet manufactured in Example 1. 4 (a) is an element mapping photograph showing the segregated state of Co corresponding to the microscopic observation photograph of FIG. 3, and FIG. 4 (b) is an element mapping photograph showing the segregated state of Cu corresponding to the microscopic observation photograph of FIG. It is a photograph. In the figure, the white part is the segregation part. To clarify the segregation state, the contrast of light and dark is changed, but R
It can be confirmed that segregation occurs along the interface of the rich phase. It was confirmed that although the inside of the R-rich phase is rich in Co, in particular, Cu segregates at the interface of the R-rich phase and an R-Co-Cu-based intermetallic compound is formed. From this, it is considered that in the present embodiment, the NdCoCu alloy is formed so as to cover the R-rich phase, which serves as a protective layer and prevents oxidation from the grain boundaries. With the elements of Nd, Fe, and O, such segregation along the interface of the R-rich phase was not seen.

FIGS. 5 and 6 show enlarged photographs of the structure of FIG. Further, in Table 1, 1-4, 5-8 described in FIG.
The results of the EDX analysis performed in the part of are shown. No. 4,
A high segregation of Co and Cu was observed at the interface of the R-rich phase of No. 8. No. Segregation of Co and Cu is observed inside the R-rich phase like the intermediate phases a of Nos. 3 and 7, but the amount of Co is larger inside and the amount of Cu segregated is larger in the intermediate phase b near the interface.
Tends to be large. This mesophase b which is unique to the present invention
Thereby, the progress of oxidation at the grain boundaries can be suppressed.

[0027]

[Table 1]

[0028]

As described in detail above, in the rare earth magnet of the present invention, in the grain boundary portion where the main phase and the R-rich phase are adjacent to each other, 1 to 20 from the grain interface toward the center of the R-rich phase.
R: 30 to 60% in the region of nm, (Co + Cu): 30
Since the R-rich phase is surrounded by an intermetallic compound of ˜60% and the balance Fe, it is a rare earth sintered magnet excellent in corrosion resistance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a positional relationship of a main phase / R rich phase / intermediate phase of the present invention.

FIG. 2 is a schematic diagram showing a positional relationship of a conventional main phase / R-rich phase / intermediate phase.

FIG. 3 is a structure observation TEM photograph in the vicinity of the R-rich phase of the present example.

FIG. 4 is an element mapping diagram showing the segregation state of Co and Cu corresponding to the structure observation photograph of FIG. 3.

5 is an enlarged TEM photograph of a main part of FIG.

FIG. 6 is an enlarged TEM photograph of a main part of FIG.

Claims (2)

[Claims] 1. R (at least one kind of rare earth element including Y) in weight%: 28 to 35%, Co: 0.5 to 5
%, Cu: 0.01 to 0.3%, M (Al,
At least one or more of Ga, Nb, and Mn): 0.3
% Or less, B: 0.8 to 1.2%, a R-Fe-Co-Cu ( -M) -B based rare-earth sintered magnet of which the remainder Fe as a main component, _R 2 _{Fe 14} B system In the grain boundary portion where the main phase and the R-rich phase are adjacent to each other, the main component is R: 30 to 60 in a region of 1 to 20 nm from the grain interface of the main phase toward the center of the R-rich phase.
%, Co + Cu: 30 to 60%, the balance Fe has an intermediate phase, and the composition ratio converted to atomic% is (Co + Cu) / R
= 0.5 to 2 is a rare earth sintered magnet having excellent corrosion resistance. 2. The rare earth sintered magnet having excellent corrosion resistance according to claim 1, wherein Dy in R is 5% or less by weight.